Millions of Americans who suffer from the uncomfortable intestinal disorder diverticulosis  more than half of the population will develop it in older age  have been told for decades to avoid eating popcorn, nuts, and that all-American favorite, corn on the cob, because those foods may compound the disorder. But a new study released this week suggests that these foods may not increase diverticulosis risk, and that in fact people who eat lots of nuts and popcorn have lower rates of the disease than others.

The study's authors, led by Dr. Lisa L. Strate, a gastroenterologist at the University of Washington, note that despite a lack of firm evidence, the conventional dietetic wisdom has prevailed among many physicians. In a recent survey as many of 47% of colorectal surgeons agreed that their patients should avoid nuts and popcorn. But Strate says the notion that these "abrasive foods" exacerbate diverticulosis is simply "an evolved theory" founded on a belief that nuts and seeds can lodge in the diverticula, the pouches or bulges that form in weak parts of the colon wall, and give the disease its name.

Diverticulosis is a baby boomer disease, prevalent among aging Westerners  one in 10 Americans over 40, both men and women, have it, according to the National Institutes of Health. By age 60, one in three Americans develop the tell-tale colonic bulges, and two-thirds of Americans over 85 suffer from the disorder, according to Strate's study. The exact causes of diverticulosis are poorly understood, Strate says, but a leading culprit appears to be the Western diet.

"This disorder is found in industrialized, western nations  nations where diets have low dietary fiber. In Africa and Asia it is very uncommon," Strate says. Reliance on refined cereal grains may be a factor, Strate says, as well as red meat consumption, obesity, smoking, lack of physical activity, and perhaps even the impact of that daily aspirin so many Americans take on their doctor's advice. More study is needed, Strate says, to pinpoint causes.

Many Americans with the disorder suffer only a few symptoms, perhaps occasional bloating in the lower abdomen or constipation. But up to 35% of people with diverticulosis will develop the more serious condition, diverticulitis, which results from inflammation of the diverticula, and causes severe pain, nausea, cramping, chills and fever, requiring invasive medical treatment such as surgery.

The annual cost of treating the more serious illness is $2.4 billion in direct health care costs, according to the study published this week in the Journal of the American Medical Association. Diverticular complications can also include bleeding and tears in the colon, which contributes to 3,400 deaths annually from the disease in the U.S. Yet the conventional wisdom that sufferers should avoid certain foods may have been upended.

Strate and her team conducted a retrospective study of a large group of men enrolled in the Health Professionals Follow-up Study; volunteers were medical providers by profession, including physicians, dentists, pharmacists and veterinarians. The group included 47,588 men aged 40 to 75 who filled out detailed questionnaires about their medical conditions and dietary habits from 1986 to 2004. Initially, the participants were free of diverticulosis or its complications. During the subsequent 18 years, 801 men developed the more serious diverticulitis and 383 reported diverticular bleeding.

Among the study participants, 27% reported eating nuts twice a week or more, the highest intake group; 15% ate popcorn or corn at least twice a week. Researchers expected to see more cases of diverticulitis among people who ate the dubious foods more often. They found just the opposite: men with the highest intake of nuts had a 20% lower risk of diverticulitis than men with the lowest intake, consuming them less than once a month. There were 133 cases of diverticulitis among the 12,928 men who ate nuts at least two times a week, versus 199 cases among the 11,860 men who ate nuts less than once a month. The same trend held for popcorn intake: men in the highest intake group were 28% less likely to develop the disease than men with the lowest intake. The study's findings about corn, however, were inconclusive, showing no statistically significant association.

Strate says it's conceivable that eating nuts may help prevent the development of diverticulitis. Nuts are rich in minerals like zinc and magnesium, which are known to contribute to a healthy colon, and they have anti-inflammatory properties. Likewise, popcorn contains lutein, a micronutrient that also has anti-inflammatory characteristics. Though many nutrition experts encourage consumption of nuts and seeds today, when the Health Professionals Follow-Up Study began in 1984, they weren't exactly considered a health food.

The bottom line, Strate says, is that perhaps "physicians should reconsider their advice"  at least for those patients who do not experience a physical worsening of symptoms or discomfort after eating particular foods. Noshing on nuts and popcorn may not worsen diverticulosis, and better yet, studies suggest that adding nuts to a healthy diet may further reduce the risk of cardiovascular disease, cancers of the colon and prostrate and diabetes.